Exposure to an RF Electromagnetic Pulse
Posted 19 mars 2026, 05:37 UTC−4 Electromagnetics, RF & Microwave Engineering, Modeling Tools & Definitions Version 6.4 3 Replies
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Hello there!
I am a newcomer to COMSOL Multiphysics and I am currently attempting to set up a simulation involving the exposure of a object to a radiofrequency (RF) electromagnetic pulse. The primary objective is to study the thermal and electromagnetic physical parameters (temperature, EF distribution). I am aware that the appropriate tool for this type of problem is the RF Module; however, I remain uncertain as to which of its physics interfaces best suits my case. Having briefly reviewed the available options, I have identified interfaces such as Electromagnetic Waves, Frequency Domain (emw) and Electromagnetic Waves, Time Explicit, among others, but I lack the background to determine which most accurately captures the physics of RF pulse propagation. I am also encountering difficulties in correctly defining the boundary conditions. Specifically, I am unsure how to set up the RF pulse excitation source and how to handle the outer boundaries of the computational domain. I have come across conditions such as Scattering Boundary Conditions and Perfectly Matched Layers (PML), which appear to be relevant for suppressing spurious reflections at the domain boundaries, but I have not yet been able to understand how to apply them correctly within the context of my model.
In light of the above, I would be most grateful if members of this community could direct me towards:
Official COMSOL tutorials or Application Library models addressing RF exposure. Should any member of the community have already addressed a similar problem and be willing to share a worked example or provide direct guidance, I would be most grateful for their contribution;
Guidance on which physics interface within the RF Module is most suitable for this class of problems;
Introductory documentation or methodological references appropriate for users approaching coupled electromagnetic–thermal modelling for the first time.
Any guidance, even of a general or preliminary nature, would be of considerable value at this stage. Thank you in advance for your time and expertise.
Kind regards
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It depends on the regimes you are trying to model. If you are working with a very short pulse (e.g., just a few cycles) then a time-domain RF model is more appropriate than a frequency domain model. If your pulse is hundreds of cycles long (or even longer) a frequency-domain RF model may be a better choice. If your object is relatively small and your illumination is plane-wave like, you may wish to expose it within a transmission-line (TL) like geometry, using a field (or port) defined at the input end, a scattering boundary (or port) at the output end, and PEC and PMC walls on the sides, according to the polarizations that go there (which you will need to specify). You will have to choose/specify the time step(s) wisely; Comol's default values for the time step will likely be useless. You will have to add a thermal time-dependent model as well and couple the multi-physics. Overall, this is not a model for beginners. Model various pieces of the physics separately first, to make sure you understand what you are doing. Also, model everything in 2D before you attempt 3D. You will need to build and study and execute many models, building toward your goal before you'll get there. Don't attempt to shortcut to a full 3D RF pulsed time-domain model including heating of the test object, all in one (your first) model. First you learn to stand, then to walk, and then to run.
-------------------Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
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Dear Robert, Thank you for your detailed and cautionary advice. I truly value the "walk before you run" approach! Anyway, just to be clear, I have spent considerable time studying other types of problems (with AC/DC module), so I would define myself as a "beginner" rather than a total novice for COMSOL..
I am currently deconstructing the model into 2D as you suggested, but I am still struggling with the practical implementation of the pulse. Since I have been working on this specific hurdle for a while, I would like to ask for your direct expertise on a few points:
- Pulse Realization: How would you practically define, for example, a nanosecond pulse in the GHz range? Do you recommend using an Analytic function (e.g., a sine wave multiplied by a Gaussian envelope) or a Piecewise function?
- Geometry Application and Context: In your previous message, you mentioned exposing the object within a transmission-line-like geometry. Is this mandatory? I would prefer to model the target object alone and "inject" the pulse from a boundary to simulate an incident wave in an open or semi-open environment. Which specific feature (e.g., Scattering Boundary Condition with Incident Field) would be most appropriate for this "direct exposure" approach?
- Boundary Conditions: How would you correctly set up the outer boundaries to ensure the pulse propagates and exits the domain without spurious reflections in a time-dependent study?
Given the complexity you mentioned, would you be willing to share a simple .mph file or a worked example of a 2D pulsed excitation? Having a "template" to study would be immensely helpful to ensure my solver settings and boundary conditions are technically sound before I attempt the thermal coupling.
I am very curious to bridge this gap. Thank you again for your patience and for sharing your time with the community.
Kind regards!
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- If you can define a smooth analytic function that represents your pulse accurately enough, then do that. Piecewise analytic, if you can't see a way to do it otherwise, but keep the connections smooth. Interpolation function may be appropriate if dealing with real-world data, but you may want to smooth-out real-world data somewhat, before using it. Note that you will need short enough time steps to properly resolve the waveform at its fastest rise & fall conditions. Do not expect the software to figure out the best choice(s) of time step(s) for you.
- Nothing mandatory. There are a lot of options and I don't have time to discuss them all (and probably couldn't do them all justice anyway). I suggest you use the simplest formulation that creates an acceptable approximation to the conditions you seek to represent. PEC and PMC boundaries yield very simple and very easily sanity-checked conditions, so don't make things more difficult for yourself unless you really need to. Scattering boundaries may be appropriate if you need to keep your illumination target from seeing unwanted strong reflections from computational boundaries, in addition to the fields from the source, but they still won't be especially good at glancing angles of incidence (which are actually fairly common). You can change the computational space geometry, material properties at boundaries, or in layers (like absorber), etc., and various settings in the code to help compensate, but often at greater computational cost. There's more to it than that but I'll stop there.
- If you conclude that you can use a TL like volume to represent your interaction after all, set TL-type ports (e.g., lumped ports, with impedances that match the TL) at each end, but if you've decided for whatever reasons that that just won't work for you, you can use scattering BCs with a non-zero applied field, or even directly define the field on a boundary without the scattering BC (but that last choice can lead to severe reflections). Also, later-time reflections can often simply be ignored (that is, by you, when interpreting the output) if you are only interested in earlier-time physics. If you want to propagate your pulse as a clean TEM plane wave, but you don't want to use a TL (or TL-like BCs) to support it, you are going to have to think more about your BCs. Selectable choices of BCs are more limited in time-domain than frequency-domain, so this may prove frustrating. Finally, remember that there exist no true "fixed finite-diameter beam" plane waves (Gaussian or otherwise) in unbound space, so you'll never really model that kind of unicorn. Don't try to fight that. Let your model obey the laws of physics while capturing the features & geometry of interest to you and ignoring the details that don't really matter.
Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
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